Prof. J. W. Judd—Statical & Dynamical Metamorphism. 249 
to be complicated and obscured by the results of other processes of 
change, than in older rock-masses of similar origin. Around volcanic 
centres, too, the rate of the rise of the temperature with descent is 
probably more rapid, and the solvent agents are more abundant than 
elsewhere; and it is also more easy to trace the effects of these agents 
upon the definite minerals making up the plutonic rocks, than in 
other cases. But all rocks at great depths must be subjected to high 
temperatures, to enormous pressures, and to some solvent agents ; 
and it may well be that at such depths a condition approaching to 
fusion or to solution may be reached, which permits of perfect re- 
crystallization of the rock materials; such a state of things would 
seem to be advocated by Dr. A. C. Lawson and Dr. G. Dawson, as 
having probably occurred in the case of the rocks which cover so 
_ large an area in Canada. 
I cannot perhaps better illustrate the complicated results of the 
joint action of statical and dynamical metamorphism than by ~ 
referring, as briefly as possible, to the cycle of changes which can 
be shown to have occurred in the case of a particular rock. 
The so-called Apatit-bringer of Oedegarden, near Bamle, in 
Norway, is a rock consisting essentially of hornblende and scapolite, 
which, as shown by the beautiful experiments of Fouqué and Michel 
Lévy, can, by fusion and slow cooling, be converted into an aggregate — 
pyroxene and felspar. That the rock was originally a pyroxene- 
felspar-rock which has been metamorphosed into a hornblende- 
scapolite one, the observations of Sjogren and others sufficiently 
indicate, and we are now able to show the exact series of processes 
by which the transformation has been effected.t 
In certain specimens the pyroxene (an enstatite) may be seen 
‘to have acquired, through a process of statical metamorphism, the 
peculiar characters of bronzite; and, by the same means, layers of 
cavities are developed along the twin-planes of the felspars, which 
cavities are filled with supersaturated solutions of sodic chloride. 
Statical metamorphism having carried the change thus far, dynamt- 
cal metamorphism has next come into play, and the bronzite has 
been converted into hornblende and the mixture of felspar and sodic 
chloride into scapolite; the former by a paramorphic, the latter by 
a metachemic transformation. At the same time the structure of the 
rock has been changed from a granitic to a granulitic one. 
This particular case is one of more than ordinary interest from 
our being able to study all the stages in the complete cycle of 
change, from a pyroxene-felspar rock to a hornblende-scapolite one, 
and back again to the former. But there are many other instances 
in which careful study may enable us to follow many of the succes- 
sive steps by which very similar changes have been gradually 
effected. 
1 Mineralogical Magazine, vol. vili. p. 186. 
